The Vital Question

Nick Lane is not just a writer of words about science, he is also a doer of experiments and a thinker of thoughts. And these days he is hot on the trail of one of the biggest ideas in the universe: the meaning of the word “life”. In this, his third book about energy and life, he comes triumphantly close to cracking the secret of why life is the way it is, to a depth that would boggle any ancient philosopher’s mind. He can now tell a story of how, when and where life started, and what happened to it in its early days. Most of that story looks as if it is true.

Life uses information (stored in DNA) to capture energy (which it stores in a chemical called ATP) to create order. Humans burn prodigious amounts of energy — we generate about 10,000 times as much energy per gram as the sun. The sun is hotter only because it is much bigger. We use energy to create and maintain intricate cellular and bodily complexity, the opposite of entropy, just as we do in the economy, where the harnessing of power from burning fuel enables us to build skyscrapers and aeroplanes. But we — and here “we” means all living creatures, including bacteria — have an idiosyncratic way of trapping energy to make it useful. We pump protons across lipid membranes.

During every second of your life you pump a billion trillion protons across membranes in the thousand trillion mitochondria that live inside your body. Mitochondria are the topic of recent parliamentary debates (about “three-parent embryos”), the central characters in this book and the descendants of bacteria. Their job is to oxidise carbon and hydrogen so as to pump protons and fuel life.

The collapse of these proton gradients is the true definition of death. Cyanide is a poison because it blocks the proton pump, and cells commit suicide (to rid the body of bad mutations) by deliberately collapsing their proton gradients. A freshly dead body is, to all intents and purposes, identical to a living one, except that on a minuscule, invisible scale, its ability to keep protons the right side of membranes has suddenly ceased.

Professor Lane, a biochemist at University College London, and his colleagues have worked out why this is and what it means. His exploration of the story takes him deep into conundrums that have fascinated human beings for millennia: species, death, sex, gender, ageing, fertility and health. In 2000 a new kind of alkaline, warm-water vent was found on the ocean floor in the mid-Atlantic (it was dubbed the Lost City because of its huge carbonate chimneys and towers), where protons diffuse across thin, semi-conducting walls of iron, nickel and sulphur into minuscule pores, causing organic molecules to accumulate and interact.

This, Lane and others now think, was how life got started some 4 billion years ago, inside these rocky pores, where the natural proton gradients came by accident to drive the generation of molecular complexity. The details of the detective story that gets him from this point to the first bacterium-like cell are challenging (to understand), intricate and compelling, but well worth the journey.

Life seems to have diverged very early on into two different kinds with different chemistry sets. We call them bacteria and “archaea”, but they both look like microbes. It was only when we read their genes that we realised how different they were — one uses right-handed forms of lipids, the other left-handed, for instance. For a staggering two billion years they were all there was on this planet. They both had great biochemical diversity but small size and structural simplicity.

Only after this time did large cells and complex creatures emerge — protozoa, plants, animals, fungi. These things have huge internal complexity in their cells as well as bodies that are often multicellular. They all share a single common ancestor because their basic machinery is always the same: plants and animals are mere variations on a theme. And yet this lurch to complexity has left little trace — there are no surviving intermediate creatures with bits of the machinery, but not other bits. How could complex (“eukaryotic”) life have sprung fully formed, like Athena from the head of Zeus?

Solving this mystery leads Lane into a world of ideas that only Lewis Carroll could make sense of. Six impossible things become believable before breakfast when you are reading a Lane book, and there are plenty here.

What seems to have happened is that a single archaeal cell engulfed a single bacterial cell that turned into a specialised energy generator and gradually passed most of its genes to the host.

This caused a problem because it brought rogue DNA sequences, or digital parasites — a bit like computer viruses — into the operating system of the host. We are still plagued by them today. They are called introns, and we deal with them by splicing them out of the transcript of DNA before using it. The machine we use to do this works slowly so it has to have a safe place to work before the transcripts get used — and that is why the nucleus evolved, to separate transcription from translation (into protein).

Having mitochondria, as the bacteria became, enabled cells to grow much larger, because the mitochondria could be numerous and small and shrink their genomes to just the essential genes — we have just 13 in ours — while the archeal genome could start to service a much larger volume and generate new kinds of machinery.

Lane’s crucial insight, his eureka moment, was when he realised that, thanks to this division of labour, the energy available per gene is hundreds of thousands of times greater in a eukaryotic cell than in a bacterium: just as the energy available per worker leapt higher in the Industrial Revolution enabling the construction of much more technology and infrastructure (my analogy, not his).

From here Lane traces the echoes of ancient struggles inside the cell, shedding light on questions such as why we have less sodium in our cells than seawater has, why pigeons live longer than rats, how species come to separate, why eggs are large and sperm small, and so on.

The material Lane has to work with is almost impossibly complicated and there are times when even the most dedicated reader will have to keep turning to the glossary to check the meaning of terms. But like the best science writers, Lane never glosses over the detail. Instead he turns it into a series of detective stories. Poirot-like he leads you from the crime to the perpetrator, from the puzzle to the solution. The difference from a detective story is that these tales are real, and fundamental to life itself.